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In computing, a meta-circular evaluator or meta-circular interpreter is an interpreter which defines each feature of the interpreted language using a similar facility of the interpreter's host language. For example, interpreting a lambda application may be implemented using function application.JOURNAL, Reynolds, John C., Definitional Interpreters for Higher-Order Programming Languages, Higher Order Symbolic Computation, August 1972, 11, 4, 363â397, 10.1023/A:1010027404223,weblink 14 April 2017, Meta-circular evaluation is most prominent in the context of Lisp. A self-interpreter is a meta-circular interpreter where the interpreted language is nearly identical to the host language; the two terms are often used synonymously.

Self-interpreters

A self-interpreter is a meta-circular interpreter where the host language is also the language being interpreted.WEB, The significance of the meta-circular interpreter,weblink 2006-11-22, Reginald, Braithwaite, 2011-01-22, A self-interpreter displays a universal function for the language in question, and can be helpful in learning certain aspects of the language.JOURNAL, Reynolds, John C., Definitional Interpreters Revisited, Higher Order Symbolic Computation, 1998, 11, 4, 356â7, 10.1023/A:1010075320153,weblink 14 April 2017, A self-interpreter will provide a circular, vacuous definition of most language constructs and thus provides little insight into the interpreted language's semantics, for example evaluation strategy. Addressing these issues produces the more general notion of a "definitional interpreter".

Uses

In combination with an existing language implementation, meta-circular interpreters provide a baseline system from which to extend a language, either upwards by adding more features or downwards by compiling away features rather than interpreting them.BOOK, Oriol, Manuel, Meyer, Bertrand, Objects, Components, Models and Patterns: 47th International Conference, TOOLS EUROPE 2009, Zurich, Switzerland, June 29-July 3, 2009, Proceedings, Springer Science & Business Media, 9783642025716, 330,weblink 14 April 2017, en, 2009-06-29, They are also useful for writing tools that are tightly integrated with the programming language, such as sophisticated debuggers.{{citation needed|date=April 2017}} A language designed with a meta-circular implementation in mind is often more suited for building languages in general, even ones completely different from the host language.{{citation needed|date=April 2017}}

Examples

{{More citations needed|section|date=September 2008}}Many languages have one or more meta-circular implementations. Here below is a partial list.Some languages with a meta-circular implementation designed from the bottom up, in grouped chronological order: